Depression affects 10-15% of all pregnant women and many of them are treated with antidepressants such as selective serotonin reuptake inhibitors (SSRIs). However, multiple studies have suggested an association between prenatal exposure to SSRIs and an increased risk of cardiovascular malformations, persistent pulmonary hypertension of the newborn and neonatal withdrawal syndrome. On the other hand, pregnant women with major depression who discontinue antidepressant therapy experience relapse of symptoms more often than those who continue on antidepressants. Because moderate to severe depression require pharmacologic treatment and many pregnancies are unplanned, the clinically relevant questions are 1) which antidepressant or SSRI to recommend for women of childbearing age and 2) whether and when to discontinue treatment during pregnancy. Despite the difficult decisions faced by patients and physicians, sufficient comparative safety and effectiveness information to guide therapeutic decisions for depression during pregnancy is lacking. Our primary objective is to provide direct evidence on the comparative effectiveness and safety of each antidepressant in a vulnerable segment of the population, i.e., low income depressed pregnant women and their children. We hypothesize that not all SSRIs are equal and that discontinuation early in pregnancy might reduce the effectiveness of treatment while reducing some risks. We propose to quantify the risk of maternal and fetal adverse events associated with continuing and discontinuing specific SSRIs during pregnancy. Within the Medicaid Analytic eXtract (MAX), a large population-based claims database linkable to additional obstetrical, birth, and psychiatric records, we will identify a cohort of over 78,000 women on SSRIs before conception who delivered between 2001 and 2007. We will compare the effectiveness and safety of continuing versus discontinuing specific SSRIs during pregnancy. We will apply an innovative combination of propensity score techniques and nested case control analyses and will obtain information from medical records to validate the outcomes and incorporate detailed clinical information, including measures of depression severity. The current proposal is an interdisciplinary collaboration between the Division of Pharmacoepidemiology and Pharmacoeconomics at Brigham and Women's Hospital, the Department of Epidemiology at Harvard School of Public Health, and the Perinatal Psychiatry Program at Massachusetts General Hospital.